1. Field of the Invention
This invention relates to electrical apparatus and more particularly although not exclusively to circuits for fluorescent laps, metal halide lamps, high pressure sodium lamps, mercury lamps and other energy efficient lamps.
2. Description of the Related Art
With existing circuits for lighting installations of the above types any additional functions such as dimming, radio frequency interference or electromagnetic interference, circuit harmonic distortion correction, power factor correction, line surge protection, soft starting, emergency back up or remote switching are normally built into the separate driver (ballast) circuits for each lamp. This causes the housing for each lamp to be unduly bulky, the circuit for each lamp to be extremely complicated and also leads to substantial costs in large installations involving many lamps. Maintenance costs are also high as the built-in functions of each ballast have to be serviced individually.